fix(home): preview locks aspect to panel dims + object-fit so it never overflows

The large FrameCard preview let the <img> drive height (`flex: 0 0
auto`, `width: auto`, `max-*: 100%`). On wide-container layouts and on
the new V2 1200×1600 dimensions the image's intrinsic size leaked
past the card, and the max-width/max-height combo can drop aspect
ratio in some browsers.

Now: the preview container locks its `aspect-ratio` to
`panelDims(model, orientation)` — same source of truth that drives the
empty-placeholder shape — and the <img> fills the container with
`object-fit: contain`. Container shape is stable whether or not the
thumbnail has loaded; image always scales to fit, portrait or
landscape device, narrow or wide phone column.

emptyAspectStyle no longer needs to carry aspect (parent already has
it); empty-preview placeholder fills 100% of the parent now.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/FrameCard.vue

@@ -89,18 +89,22 @@ const props = defineProps<{
 
 defineEmits<{ 'add-photo': [deviceId: number]; edit: [deviceId: number] }>()
 
-// On large cards we let the <img> drive the preview height (its intrinsic
-// aspect ratio is the device's actual aspect). Until the image loads — or
-// when no thumbnail exists yet — we want the empty placeholder to reserve
-// roughly the same shape so the layout doesn't jump.
-const previewStyle = computed(() => ({}))
-
-const emptyAspectStyle = computed(() => {
+// Large cards lock the preview's aspect to the panel's actual dimensions,
+// independent of whether the image has loaded. That way the layout never
+// jumps when the thumbnail arrives, the <img> can use object-fit: contain
+// to scale down inside the container without overflow, and both portrait
+// and landscape devices fit cleanly inside whatever their parent column
+// allows.
+const previewStyle = computed(() => {
   if (props.size !== 'large') return {}
   const { width, height } = panelDims(props.model ?? 'v1', props.orientation)
   return { aspectRatio: `${width} / ${height}` }
 })
 
+// Empty-preview placeholder fills its parent (which already has aspect set
+// by previewStyle), so nothing extra needed here.
+const emptyAspectStyle = computed(() => ({}))
+
 const statusText = computed(() => {
   switch (props.status) {
     case 'ok':        return 'Online'
@@ -190,26 +194,27 @@ const statusText = computed(() => {
     height: 100%;
   }
 
-  // Cap the preview height so portrait frames (3:5) don't blow past half
-  // the viewport. Landscape frames (5:3) at full card width are short enough
-  // that the cap never engages. The photo is centered within the preview;
-  // portrait shots get a thin grey bar on each side instead of stretching.
+  // Preview locks to the device's actual aspect via inline aspect-ratio set
+  // by previewStyle. Caps height at 40dvh so a portrait frame's tall aspect
+  // doesn't push everything else below the fold; `min-width: 0` lets flex
+  // shrink it on narrow containers.
   &--large &__preview {
     flex: 0 0 auto;
+    width: 100%;
+    min-width: 0;
+    max-height: 40dvh;
     background: var(--color-surface-2);
     display: flex;
     align-items: center;
     justify-content: center;
     overflow: hidden;
-    max-height: 40dvh;
   }
 
   &--large &__img {
     display: block;
-    max-width: 100%;
-    max-height: 100%;
-    width: auto;
-    height: auto;
+    width: 100%;
+    height: 100%;
+    object-fit: contain;
   }
 
   &--large &__empty-preview {
@@ -219,6 +224,7 @@ const statusText = computed(() => {
     align-items: center;
     justify-content: center;
     width: 100%;
+    height: 100%;
   }
 
   &--large &__body {

frontend/src/test/components/FrameCard.test.ts

@@ -146,35 +146,34 @@ describe('FrameCard', () => {
     expect(wrapper.emitted('edit')![0]).toEqual([1])
   })
 
-  it('reserves a V1 landscape (1600 × 960) placeholder when no thumbnail is present', () => {
+  // Aspect ratio is set on the preview container itself (not the placeholder)
+  // so the box shape is stable whether or not the thumbnail has loaded —
+  // image inside scales with object-fit: contain.
+  it('locks preview aspect to V1 landscape (1600 × 960)', () => {
     const wrapper = mount(FrameCard, {
       props: { ...defaultProps, size: 'large', orientation: 'landscape', model: 'v1' },
     })
-    const empty = wrapper.find('.frame-card__empty-preview')
-    expect(empty.attributes('style')).toMatch(/aspect-ratio:\s*1600\s*\/\s*960/)
+    expect(wrapper.find('.frame-card__preview').attributes('style')).toMatch(/aspect-ratio:\s*1600\s*\/\s*960/)
   })
 
-  it('reserves a V1 portrait (960 × 1600) placeholder when no thumbnail is present', () => {
+  it('locks preview aspect to V1 portrait (960 × 1600)', () => {
     const wrapper = mount(FrameCard, {
       props: { ...defaultProps, size: 'large', orientation: 'portrait', model: 'v1' },
     })
-    const empty = wrapper.find('.frame-card__empty-preview')
-    expect(empty.attributes('style')).toMatch(/aspect-ratio:\s*960\s*\/\s*1600/)
+    expect(wrapper.find('.frame-card__preview').attributes('style')).toMatch(/aspect-ratio:\s*960\s*\/\s*1600/)
   })
 
-  it('reserves a V2 portrait (1200 × 1600) placeholder when no thumbnail is present', () => {
+  it('locks preview aspect to V2 portrait (1200 × 1600)', () => {
     const wrapper = mount(FrameCard, {
       props: { ...defaultProps, size: 'large', orientation: 'portrait', model: 'v2' },
     })
-    const empty = wrapper.find('.frame-card__empty-preview')
-    expect(empty.attributes('style')).toMatch(/aspect-ratio:\s*1200\s*\/\s*1600/)
+    expect(wrapper.find('.frame-card__preview').attributes('style')).toMatch(/aspect-ratio:\s*1200\s*\/\s*1600/)
   })
 
-  it('reserves a V2 landscape (1600 × 1200) placeholder when no thumbnail is present', () => {
+  it('locks preview aspect to V2 landscape (1600 × 1200)', () => {
     const wrapper = mount(FrameCard, {
       props: { ...defaultProps, size: 'large', orientation: 'landscape', model: 'v2' },
     })
-    const empty = wrapper.find('.frame-card__empty-preview')
-    expect(empty.attributes('style')).toMatch(/aspect-ratio:\s*1600\s*\/\s*1200/)
+    expect(wrapper.find('.frame-card__preview').attributes('style')).toMatch(/aspect-ratio:\s*1600\s*\/\s*1200/)
   })
 })